



class Solution:

    def mergeTwoLists(self, l1, l2):

        # 处理递归的边界条件
        if not l1:
            return l2
        if not l2:
            return l1
        
        # while True:
        # 使用递归
        if l1.val <= l2.val:

            l1.next = self.mergeTwoLists(l1.next, l2)
            return l1
        else:
            l2.next = self.mergeTwoLists(l1, l2.next)
            return l2

        
            


